1. Field of the Invention
The present invention relates generally to fastener tension sensing systems and more specifically to a RFID torque sensing tag system for fasteners.
2. Background of the Invention
Fasteners such as bolts, nuts, studs, washers, rivets, and the like are used in innumerable structures and machines. The need for improved fastener tension sensing systems is driven by costly documented failures in a wide range of application and for many different causes. Fastener failure analysis has shown that the causes include, but are not limited to, improper tightening, fatigue, tensile fracture, galling, insufficient preload, thread stripping, creep, stress relaxation, and self-loosening.
In many disasters related to fastener failures, better inspection could have been used to identify problems before failure. Such disasters include bridges, tunnels, and train rails where fastener failures are known to have caused disastrous results. Automotive failures occur due to common problems such as lug bolt failures in automotive racing. Aircraft are some of the most intensely inspected products in existence but entire fleets have been grounded due to loose bolts in certain subassemblies. Theme park accidents have been caused by fastener failures.
Accordingly, those of skill in the art acknowledge a long felt need exists for a relatively inexpensive fastener system to initially check recently installed fasteners and to monitor over time the tension of standard off the shelf or unmodified fasteners with minimal material costs and reduced labor costs.
However, the prior art does not teach such a system. Verifying that multiple fasteners are properly torqued, compressed, or otherwise secured to the desired tension to apply the required force is typically a labor intensive and/or expensive proposition.
Given the disasters that have occurred due to fastener failures, prior art attempts have been made to provide tension sensors that provide a wireless indication of the tension status of the fasteners. However, prior art fastener torque sensors tend to be expensive, complicated, and/or require modification of the fasteners. For example, US patent application 2013/0068011, also discussed below, teaches a rather complex housing mounted on each bolt with external wiring required to each pressure transducer, requires an external power source for each fastener, wiring connections between transponder and torque sensor, a transponder to communicate to communicate with an external base station, a controller circuit to compare the current tension with an initial tension, and also an RFID tag to uniquely identify each bolt. Such a system is likely to be cost prohibitive for most applications. Another example of prior art is US patent application 2013/0047408, also discussed below, which teaches an embedded ultrasonic transducer in the head of the bolt making the modified bolts expensive. Such a system is associated with very close read ranges, likely involving contact with the fastener. Integration of an RFID circuit with a bolt typically implies that the embedded RFID circuit will have a very small antenna and hence will be very range limited.
An RFID system comprises an interrogator, also called a reader, and a wireless tag wherein the interrogator transmits a signal to the tag, and the tag returns the desired information by radio wave. RFID technology enables the reading of multiple wireless tags, perhaps thousands of wireless tags at the same time or in a desired sequence. RFID devices may or may not utilize batteries. Strictly passive RFID tags require no active electronic circuits, such as power absorbing electronic switches. On the other hand, pseudo-passive RFID tags rectify the electromagnetic wave transmitted by the interrogator, and then use this power for operating integrated circuits. The primary advantages of the strictly passive and pseudo-passive tags are the independence from a battery, and typically lower weight and size. These RFID tags are also less costly, often to the extent to which they are deemed disposable. However, the prior art does not provide a way to utilize RFID technology for a low priced torque sensor that utilizes standard fasteners.
The following prior art patents and applications disclose various types of torque sensing systems, but do not address the problems discussed hereinbefore:
U.S. Pat. No. 8,156,820, issued Apr. 17, 2012 to Dral et al., discloses a device and method for tightening a bolt or a nut threaded on its end, which end extends through at least a first body and screws into a hole in a second body or extends through the second body into another nut. The device has gripping means co-acting with the bolt-head or the nuts. Means process a signal generated by sensor means subject to the axial force exerted on the surface of the first body by the bolt-head or the first nut, or on the surface of the second body by the second nut, and control the device such that the bolt-head or a nut is tightened subject to the axial force exerted on the surface of one of the bodies, which sensor means are in an annular body around the threaded hole between the bolt-head or first nut and the first body or between the second nut and second body.
U.S. Pat. No. 7,698,949, issued Apr. 20, 2010 to Akdeniz, et al., discloses apparatus, systems, and methods for inspecting and monitoring bolted joints of metallic and composite structures for defects such as delamination and fatigue cracking are provided that incorporate ultrasonic transducers with load bearing washers. These active washers may be used for inspecting and monitoring a structure beneath such load bearing fasteners as bolts and nuts. Active washers may be used for continuous, periodic, and controlled inspections of bolted joints. Ultrasonic transducers may be permanently applied to a surface of a washer or recessed in a cavity on a surface of the washer. Inspection signals may be transmitted from ultrasonic transducers into a structure and reflected in pulse-echo application or received by another active washer on the opposing side of the structure in a through-transmission application.
U.S. Pat. No. 7,644,627, issued Jan. 12, 2010 to Kibblewhite, et al., discloses thread forming fasteners for ultrasonic load measurement and control. An ultrasonic load measurement transducer is mated with a thread-forming fastener to provide a load indicating thread-forming fastener that can be used for the precise and reliable assembly of critical bolted joints, such as those in the automobile and aerospace industries, among others. Steps can then be taken to accurately measure and control the load in the thread-forming fastener during tightening, and to inspect the load in the thread-forming fastener after assembly. A similar result can be achieved for a thread-locking fastener by mating an ultrasonic transducer with the thread-locking fastener assembly.
U.S. Pat. No. 7,520,175, issued Apr. 21, 2010 to Matsukawa, et al., discloses a strain sensor whereby a fixing member is composed of an upper washer and a lower washer; and a sensor substrate is sandwiched and held by the upper and lower washers. A strain-detecting element is disposed on the sensor substrate. A strain sensor as configured above is fixed onto a measurement target via the fixing member. Accordingly, the strain sensor does not generate an output signal when no external force is applied, demonstrating stable characteristics.
U.S. Pat. No. 7,293,466, issued Nov. 13, 2007 to Ohta, et al., discloses a bolt with a function of measuring strain, comprising a Wheatstone bridge circuit comprising a strain sensor and a dummy resistor, a translate circuit that amplifies a signal from the Wheatstone bridge circuit to convert the same into a digital signal, a transmitting circuit that transmits the digital signal outside the bolt, and a power circuit, by which electromagnetic wave energy received from outside the bolt is supplied as a power source for at least any one of the circuits.
U.S. Pat. No. 6,658,924, issued Dec. 9, 2003 too Shirato, et al., discloses a method for measuring dynamic characteristics of a wheel of a vehicle. A washer-type strain sensor, which generates an output representing a load acting thereon, is arranged between the vehicle body and the wheel. A dynamic load acting on the wheel is measured on the basis of the outputs of the strain sensor when the vehicle is traveling. A lateral force, a lateral-force coefficient, a slip angle, and steering characteristics of the wheel are obtained on the basis of the measured dynamic load, and thereby the cornering characteristics of the wheel are obtained.
U.S. Pat. No. 6,575,039, issued Jun. 10, 2003 to Murai, et al., discloses a combustion pressure sensor assembly. A glow plug with combustion pressure sensor having a plug body having a screw portion on the outer peripheral surface is inserted into a screw hole of an engine head and screw-connected to it, a combustion pressure sensor fixed to the plug body to which the plug body is inserted, and a lead wire for leading out the sensor signal connected to the sensor, wherein the outside diameter of a hexagonal portion used for screw connection between the plug body and the screw hole out of the plug body is smaller than the inside diameter of a through hole of the combustion pressure sensor so that the plug body can be inserted into the combustion pressure sensor from the hexagonal portion end.
U.S. Pat. No. 5,970,798, issued Oct. 26, 1999, Gleman, et al., discloses an ultrasonic bolt gage which uses a cross-correlation algorithm to determine a tension applied to a fastener, such as a bolt. The cross-correlation analysis is preferably performed using a processor operating on a series of captured ultrasonic echo waveforms. The ultrasonic bolt gage is further described as using the captured ultrasonic echo waveforms to perform additional modes of analysis, such as feature recognition. Multiple tension data outputs, therefore, can be obtained from a single data acquisition for increased measurement reliability. In addition, one embodiment of the gage has been described as multi-channel, having a multiplexer for performing a tension analysis on one of a plurality of bolts.
U.S. Pat. No. 5,675,087, issued Oct. 17, 1997 to MacLaughln, et al., discloses a device for measuring a load on a part and for monitoring the integrity of the part such as a bolt, comprises a socket having walls defining an interior space wherein the socket engages the bolt for transmitting a load to the bolt. An electromagnetic acoustic transducer comprising a magnet and a coil is located in the interior space of the socket near the bolt. The coil provides a current while the magnet provides a magnetic field such that the magnet and the coil generate an ultrasonic signal within the bolt. A detector is used to detect and measure a change in the ultrasonic signal at the bolt for measuring the load on the bolt and for detecting any flaws in the bolt.
U.S. Pat. No. 5,499,540, issued Mar. 19, 1996 to Whaley, et al., discloses a device for measuring a load on a part such as a bolt, comprises a socket having walls defining an interior space wherein the socket engages the bolt for transmitting a load to the bolt. An electromagnetic acoustic transducer comprising a magnet and a coil is located in the interior space of the socket near the bolt. The coil provides a current while the magnet provides a magnetic field such that the magnet and the coil generate an ultrasonic signal within the bolt. A detector is used to detect and measure a change in the ultrasonic signal at the bolt.
U.S. Pat. No. 5,437,525, issued Aug. 1, 1995 to Bras discloses a force sensor for measuring tightening tension applied to an assembly component having first and second faces and an axis of symmetry includes a ceramic support layer having a mounting side to be secured to the first face and an exposed side carrying a piezoresistive layer having a resistance that varies in response to its deformation. The force sensor may comprise a central metallic layer and an annular metallic layer joined by the piezoresistive layer or at least two separate sensors having angularly disposed longitudinal axes. A machine for tightening the assembly component includes a motor driven socket for torqueing the component in accordance with a sensed tightening tension.
U.S. Pat. No. 5,392,654, issued Feb. 28, 1996 to Boyle discloses a rock bolt load sensor assembly for use to determine the load on a nut screwed onto a bolt embedded in a rock face, the assembly comprising a plurality of spring washers arranged to be mounted on the bolt between the nut and a roof plate, and a sensor comprising an induction coil adapted to be, in use, placed around the washers, the sensor including an indicator coupled to the induction coil whereby in use, the spring washers define an air space which varies in dependence on the load on the bolt and the induction coil provides an electrical indication of variation of the air space and the indicator provides an indication of variation of the load on the bolt.
U.S. Pat. No. 5,343,759, issued Sep. 6, 1994 to Hesthamar et al., discloses a sensor system for measuring e.g. the preloads in screws, bolts or similar. It comprises sensor means comprising a magnetoelastic material sensitive to the preloads to which the object is exposed and a sensing device comprising a contact portion and gripping portion. The contact portion is so arranged that it at least partly surrounds the sensor means and the magnetoelastic material is excited with an excitation frequency of at least 300 kHz.
U.S. Pat. No. 5,323,643, issued Jun. 28, 1994 to Kojima, et al., discloses a device for detecting a change in internal pressure of a cylinder includes a cylinder head, an ignition plug threadingly fitted into a plug insertion hole of the cylinder head. An annular piezoelectric sensor is secured in the plug insertion hole by screwing the plug into the insertion hole. The sensor has such an outer periphery that, when the ignition plug is screwed into the plug hole, a part of the outer periphery of the sensor placed is brought into engagement with an inside periphery of the plug hole and is thereby prevented from being further rotated in the screwing direction. By using a gasket having the same relative shape to the periphery of the plug insertion hole as that of the above sensor, rotation of the sensor can be prevented even when the sensor does not have such a relative shape.
U.S. Pat. No. 4,760,740, issued Aug. 2, 1988 to Mesiterling discloses a vacuum coupled ultrasonic transducer is presented for coupling a transducer to a bolt for ultrasonic measurement of bolt elongation. A central passageway extends through the transducer body, the piezoelectric crystal and a seal element. A vacuum line extends through the central passageway.
U.S. Pat. No. 4,553,124, issued Nov. 12, 1985 to Malicki discloses a strain gauge transducer which is utilized with a bolt to sense loading and has a construction which permits accurate axial alignment, testing before installation, removal for inspection and any necessary repair. The transducer includes a body having a web extending between a threaded inner end and an enlarged outer head. An annular seat on the head engages a bolt hole surface as the threaded inner end is received by a threaded portion of the bolt hole. At least two strain gauges are utilized with each mounted on one of the parallel web surfaces, and wires connected to the strain gauges extend through a wire passage in the enlarged head to permit a signal to be sensed by the strain gauges and fed to suitable instrumentation. In the preferred construction, the web has a thickness in the range of about 0.020 to 0.060 of an inch and most preferably, about 0.040 of an inch in order to minimize twisting of the web upon installation while still providing accurate readings that are not substantially affected by bending loading. Round inner and outer portions provide uniform loading of the web without any stress concentrations.
U.S. Pat. No. 4,295,377, issued Oct. 20, 1981 to Couchman discloses a threaded fastener incorporating a removable ultrasonic transducer for obtaining preload measurements as well as other measurements for quality control inspection or for monitoring purposes. The transducer may be removed for repair or replacement purposes.
U.S. Pat. No. 4,062,227, issued Dec. 13, 1977 to Heyman discloses a CW ultrasonic device for measuring frequency shifts of the peak of a mechanical resonance in a body. One application of the device is measuring the strain in a bolt. It also has other applications such as measuring the thickness of a body, measuring the depth of a flaw in a body, measuring the elongation of body and measuring changes in velocity of sound in a body. The body is connected, by means of a CW transducer, to electrical circuit means including a narrow band RF amplifier to form a closed loop feedback marginal oscillator that frequency locks the device to the peak of a mechanical resonance in the body. Thereafter, when the frequency of this peak changes, because of a physical change in the body, the frequency of the oscillator changes. The device includes an automatic frequency resonant peak tracker that produces a voltage that is related to a change in frequency of the oscillator. This voltage is applied to the RF amplifier to change the center of its frequency band to include the frequency of the peak and is a measure of the frequency shift. The device also includes a special transducer which requires contact to only one side of the body and provides high electrical isolation between its parts.
Japanese Patent No. 11-118637 issued Oct. 15, 2007 to Yoshihiri discloses a sensor bolt. To the bottom part of a through hole formed from the side of the head part of a sensor bolt, a sensor such as a distortion gage is mold-adhered. In addition, the output of an amplifier housed in the recessed part of the head part is connected to an indicator such as an LED. The sensor bolt is inserted into the hole of a body to which a bolt is tightened and is tightened with a nut, and the sensor detects a generated tightening axial force and outputs an electric signal. The amplifier amplifies and compares it with an optimum set tightening value set in advance. In other words, as the electric signal is smaller than the optimum set value at the beginning of tightening, the indicator is lighted, and at the time when the electric signal reaches the optimum set value with the gradual tightening, the indicator is turned off. In the case that the tightening is excessive above the optimum set value, the indicator is lighted.
Japanese Patent Application No. JP2005114441 published Oct. 6, 2003 to Hiroyuki, et al., discloses an electric circuit driven by the power supplied by any one of electromagnetic coupling, electromagnetic induction, microwave power dispatching, and optical coupling. A Wheatstone bridge constituted in the impurity dispersion layer of a silicon substrate is embedded in the bolt. The power supply system without wiring makes it simple and long life. A dummy resistor for constituting the Wheatstone bridge is embedded in the bolt, thereby the high precision measurement can be performed even in the case that the temperature is changed.
Japanese Patent Application No. JP2002004798 published Jun. 22, 2000 to Akira, et al., discloses a fastening and strain sensing system using a fastening body. A strain sensing system comprises a bolt, a nut, and a spacer installed between the nut and a body to be fastened and a transponder which uses a fastening body capable of sensing a strain which occurs in the axial direction of the bolt.
United States Patent Application No. 20130068031 filed Mar. 21, 2013 to Mekid, et al., discloses a bolt tension monitoring system that provides remote monitoring of the tension of a bolt, thus allowing for remote monitoring of general structural health and integrity of the fastener. The bolt tension monitoring system includes a housing adapted for being retained on a head of a bolt to be monitored. The system further includes a force transducer positioned between the head of the bolt and a surface in which the bolt is fastened and measures tension between the head of the bolt and the workpiece surface. A controller circuit within the housing calculates the difference between currently measured tension between the head of the bolt and the workpiece surface and an initially measured tension. A wireless transponder mounted in the housing transmits an alert signal if the calculated difference exceeds a pre-defined threshold value.
United States Patent Application No. 20100054891 filed Mar. 4, 2010 to Nishida, et al., discloses a detecting system of a fastening apparatus that detects an axial force of the fastening apparatus including a bolt or a nut. The detecting system includes an axial force detector including a strain gauge and an IC tag, the strain gauge being provided at a predetermined location to detect an axial force value of the fastening apparatus, and the IC tag being connected to the strain gauge and wirelessly transmitting the detected axial force value and unique identification information. Power is supplied to the axial force detector. A reader reads data transmitted from the axial force detector.
United States Patent Application No. 20100261578 filed Oct. 14, 2010 to Fujii, et al., discloses a load sensor assembly for measuring an amount of torque transmitted through a torque establishing element that includes a core mounted on a transmission housing and a load sensor mounted on the core. The load sensor is positioned against a portion of the torque establishing element whereby a portion of the amount of torque transmitted through the torque establishing element travels through the load sensor and is measured. A cable is connected to the load sensor for transmitting a signal representative of the amount of torque to a transmission controller.
United States Patent Application No. 20080278319 filed Nov. 13, 2008 to Meiksin, et al., discloses a detection and alarm system comprising a piezoelectric film sensor and associated circuitry. The sensor detects acoustic emission signals from metallic objects under stress upon which it is affixed. The associated circuitry receives electronic signals from the sensor, creates and evaluates a sensor output value including rate ratio and frequency content of such signals within preset time limits. This data allows the detection of impending failure, an alarm condition, of the metallic object by identifying significant changes in the rate of emission of such sensor signals. An alarm condition may then trigger an alarm signal to warm of such impending failure.
As seen from above, the prior art does not teach how to provide a low cost torque monitoring system using strictly or pseudo passive wireless tags that operates with standard off the shelf or unmodified fasteners. Moreover, even the above discussed art that utilize RFIDs require relatively expensive modified bolts that have a very limited range of transmission so that the fastener torque sensing systems are not only expensive but have significantly limited functionality. Accordingly, those of skill in the art will appreciate the present invention that addresses the above and other problems.